Filling apparatus for nuclear fuel pellets or the like

ABSTRACT

A filling apparatus for inserting material in pellet form into long envelope tubes where the pellets have a diameter that insures a close fit with respect to the inner wall of the envelope tube has a magazine for holding a large number of stacks of the pellets and a guide structure connectable to the magazine for holding and guiding the stacks individually. An insertion mechanism is disposed in operative proximity to the guide structure for inserting the stack disposed in the guide structure into one of the envelope tubes to be filled. The insertion mechanism includes a tubular housing, a pusher slidably disposed in the housing and a drive device which engages the pusher for reciprocally moving the pusher to push the pellet stack from the guide structure into the envelope tube.

United States Paw... v r Q ca ROOM 7 v Hotz 1 July 17, 1973 [54] FILLINGAPPARATUS FOR NUCLEAR FUEL l,578,072 3/1926 Canning et al 2l4/34 PELLETSOR THE LIKE [75] Inventor: Karl l-lotz, Erlangen, Germany PrimaryExaminer-Robert Sheridaf Att0rneyCurt M. Avery, Arthur E. wllfond,Daniel J. [73] Assignee: Siemens Aktiengesellschaft, Tick and Herbert LLerner Erlangen, Germany [22] Filed: Dec. 8, 1970 57 T C PP 96,175 Afilling apparatus for inserting material in pellet form into longenvelope tubes where the pellets have a diam- [30] Foreign ApplicationPriority Data eter that insures a close fit with respect to the innerwall of the envelope tube has a magazine for holding a large Dec. 9,l969 Germany P 19 61 575.9 number of stacks of the pellets and a guideStructure connectable to the magazine for holding and guiding [52] Cl214/34 gl7 g the stacks individually. An insertion mechanism is dis-[51] Int Cl 621C 19/06 posed in operative proximity to the guidestructure for Fie'ld CN 18 R inserting the stack disposed in the guidestructure into I 214/23 226/l72 one of the envelope tubes to be filled.The insertion mechanism includes a tubular housing, a pusher slid-References Cited ably disposed in the housing and a drive device whichengages the pusher for reciprocally moving the pusher UNITED STATESPATENTS to push the pellet stack from the guide structure into 2,725,993l2/1955 Smith 214/18 N X th envelope tube, 3,009,868 ll/l96l Moulin176/30 3,567,095 3/1971 Geist et a] 226/172 7 Claims, 2 Drawing FiguresL JLZL Patented July 17, 1973 l/l/IY/ I FILLING APPARATUS FOR NUCLEARFUEL PELLETS OR THE LIKE My invention relates to a filling apparatus forinserting pellet-shaped material into long envelope tubes. The pelletshaving a diameter substantially the same as the inner diameter of thetube so that a close fit between the pellets and the inner wall of theenvelope tube is insured. The filling apparatus of my invention isespecially suitable for use in connection with pellets of nuclear fuelmaterial. Since the diameter clearance between the pellets and theenvelope tube lie only in the order of magnitude of l l mm, a smallfragment split off from a pellet can cause damage to theinner wall ofthe envelope tube as well as cause a severe impediment in the tubefilling procedure. It is therefore necessary to provide for the completemechanization of the filling proceudre. This is also necessary in viewof the size of the tube to be filled, such tubes having a length of upto 5 m and a diameter of from to mm.

Up to the present time, it has been conventional to use so-calledfilling tappets. These tappets are used to insert in a horizontalposition pellet columns into envelope tubes. The pellet columns are puttogether outside of the tube and have a length of 30 cm. This result canbe achieved with one of two methods. One arrangement involves applyingthe same tappet stroke and using a relatively short tappet rod. Thetappet would be required to move an ever longer pellet column in theenvelope tube and this has as a consequence that an ever increasingfriction force and likewise an ever increasing insertion force must beapplied to the tappet. This arrangement not only places greatrequirements on the holding of the envelope tube to be filled, but alsointroduces the danger that the pellets will become damaged within theenvelope tube so that under certain circumstances the entire fillingprocedure as well as the later operation of the finished fuel rods canbe affected.

The other or second arrangement is that a very long tappet can be usedto urge the pellet stacks or pellet columns to their final position inthe envelope tube. With this arrangement, no increase in the frictionwithin the envelope tube arises and the pressure load is always the sameand does not increase. Accordingly, the possibility of damage isprecluded. However, this arrangement requires the use of a very longtappet,'so that aside from space needed for accommodating such a fillingapparatus, there is the danger of bending the long rod.

It is an object of my invention to improve upon the stacks of pelletsand is-provided with aguide structure connectable to the magazine forholdingand guiding the stacks individually. An insertion mechanism isdisposed in operative proximity to the :guide structure for insertingthe stack disposed in the guide structureinto an envelope tube to befilled. Theinsertion mechanism includes a tubular housing, a pusherslidably disposed in the housing and a drive that engages the pusher forreciprocally moving the same to push the tappet from the guide structureinto the envelope tube to be filled.

According to another feature of the invention, the filling apparatus isprovided with an enclosure surrounding the magazine, guide structure andinsertion mechanism in gas-tight relation to the ambient. The enclosureis provided with a suitable means for evacuating and for filling thesame with protective gas. Also provided is a receiving structuredisposed on the enclosure for receiving the envelope tube to be filledin gastight relation to the ambient.

According to a further feature of the invention, the tubular housing isgiven a curved shape which permits the apparatus of the invention to beaccommodated in a limited space. Also, the pusher can be a beaded chainthat fits snugly in the housing and the drive can be a drive belt inlateral engagement with the beaded chain.

In place of a rigid tappet rod, the aforementioned flexible beaded chainis provided which, in contrast to the tappet rod, can be installed inminimal space and the bending of the chain is prevented with a simpleretaining structure such as, for example, a tubular housing. The frontpusher piece of such a beaded chain can be directed with practically noplay at all, so that the insertion path for the pellet column can beprecisely adjusted. This adjustment results in a measurement of thelength of the insertion path and the measurement can be carried out withimpulses.

The invention will now be described with reference to the drawingwherein FIG. 1 is an elevation view, partially in section, of a fillingapparatus according to the invention; and

FIG. 2 is a plan view, partially in section of the filling apparatusillustrated in FIG. 1.

The-tube to be filled is connected to the gas-tight enclosure 23. Notillustrated, is a vacuum pump and a protective gas source which areconnectable to the enclosure at passage means 43. Within the enclosure23, there is located a nuclear pellet magazine 21 containing a row ofprearranged columns of nuclear fuel pellets 2. The pellet columns thatin turn are brought to lie in front of the envelope tube 1 are insertedinto the tube 1 by the action of the bead chain 3. The envelope tube .1is connected with an enclosure feed 24 in gas-tight relation to theambient. The drive for the bead chain is disposed in a separateenclosure'42 and comprises rollers 4 on which drive belts 41 are mountedas illustrated. It is possible to drive either one or both drive beltsby a drive motor via a slipping clutch so that the bead chain 3 ismovable in either the forward or backward direction. The bead chain hasa head 34 in which a cord 33 is secured. Sphere-like beads 31 andtube-like beads 32 are alternately strung on the cord 33. At the end ofcord 33, the chain is held tight and at the same time elastic by aspring 35. In lieu of the spring 35 a stretchable elastic cord 33 couldbe used.

Outside of the enclosure 42 provided for the drive, a tubular guide 36is provided for guiding 'the'bead chain. The tubular member 36 is closedgas-tight at its end so that the insertion procedure can be undertakenin a controlled atmosphere, so that neither the pellet column to beinserted into the envelope tube I 'nor the 'bead chain 3 can bend out ofline 'before the pellet column'is introduced in the envelope tube 1,there isprovided within the magazine housing 23, a guiding and holdingstructure 23 that can, for example, be constructed from sheetmetalcurved to correspond to the pellet diameter as well as being providedwith a spring guide. To minimize friction, the magazine grooves in whichthe pellet columns 2 are disposed can be prismatically dimensioned. Thematerial to be used to construct the grooves is determined by the pelletmaterial. According to the application purpose of the fuel rods producedby this filling apparatus and procedure, the pellets can be made ofmaterial containing uranium or plutonium containing material andrepresent, for example, oxides, carbides or cermets. It is possible toexpand the illustrated apparatus so that after the envelope tube isfilled with the nuclear fuel material pellets in accordance with theprinciple delineated above, it is possible to insert still other bodiesinto the tube, for example, bodies made of ceramic, hollow members orsprings. It is also possible to apply the end cap to the tube to befilled and, for this purpose, the envelope tube extension piece orenclosure feed 24 must be constructed in a different manner.

The profile belts for driving the bead chain 3 can, for example, beconfigured as a metal link chain or be made of a corresponding rubberprofile or another elastic material. Basically, it is sufficient to onlydrive a single belt even though it is advantageous to drive all profilebelts standing in engagement with the bead chain. As. already mentioned,a slip clutch is arranged between the drive rollers 4 and the motor. Theclutch has a coupling force that is adjusted so that, in the event thatan impediment arises during the loading of the pellet stack, damage tothe latter is prevented. If desired, the slip coupling can be connectedtogether with a signal apparatus which is actuated when such a situationoccurs. In addition it is advantageous to permit the motor to rotate ina single direction and to provide a reversal mechanism that has a propergearing ratio for providing a quick return of the bead chain. Thecoupling can also be used for bringing the filling apparatus to rest.

To operate the filling apparatus according to the invention, theenvelope tube to be filled is provided with a vacuum tight stop at oneend and secured to the enclosure at its other end. The apparatus andenvelope tube are then evacuated. THe magazine is moved forward so thatfirst row of nuclear fuel material pellets 2 are disposed in front ofthe envelope tube 1. The motor M is then placed in operation, the motormoving the bead chain 3 forward. The head chain 3 then comes intocontact with the pellet stack 2 and pushes the latter into the envelopetube until the pellet stack comes in conatct with the end stop securedat end of the tube. The bead chain is then pulled back in a fast gearand the magazine 21 moves one position further and the bead chain 3moves slowly foward to perform the filling procedure. The second pelletstack is then pushed forward until it is brought into contact withpellet stack already inserted in the envelope tube and the bead chain isagain withdrawn in the fast gear. This procedure is repeated until theenvelope tube is filled. Then the helium gas is permitted to fill theapparatus and penetrates also into the fin spaces between inner wall ofthe envelope tube and the pellets. Finally, an end stopper is placed inthe end of the envelope tube which is still free and welded thereto. Thehelium filling enables the user to detect possible locations at whichthe fuel rod construction is not gas-tight. The helium filling also hasthe task of improving the heat transfer, during operation of the nuclearreactor, between the pellets and the envelope tube. The pellets andenvelope tube have different coefficients of heat expansion. Thespecific configuration of the magazine 21 is dictated by the size andtype of pellets to be inserted into the envelope tube as well as thetechnique used to produce the pellets. The pellets can be formed intablet fonn or also in cylindrical configuration and are then providedwith a guiding jacket.

. While the invention is described by means of specific example, I donot wish to be limited thereto, for obvious modifications will occur tothose skilled in the art without departing from the scope of theinvention.

I claim:

1. Filling apparatus for inserting into long envelope tubes a material,such as nuclear fuel, in the form of pellets having a diameter thatensures a close fit with respect to the inner wall of the envelope tube,said apparatus comprising a magazine for holding a large number ofstacks of the pellets, a guide structure connectable to said magazinefor holding and guiding said stacks individually, and insertion means inoperative proximity to said guide structure for inserting the stackdiposed in said guide structure into an envelope tube to be filled, saidinsertion means including a tubular housing having a curved shape,flexible elongated insertion means slidably disposed in said housing,said insertion means comprising a beaded chain having a curved shape,and drive means engaging said insertion means for reciprocally movingsaid insertion means into the envelope tube to move said tablet stackfrom said guide structure into the envelope tube to a selected locationtherein, each successive stack being moved individually by saidinsertion means into the envelope tube, said drive means including adrive belt in lateral engagement with said chain.

2. Apparatus according to claim 1, said drive means including a seconddrive belt, a slipping clutch, and a drive mechanism coupled with atleast one of said drive belts via said clutch, said drive mechanismincluding control means for controlling the speed at which said onedrive belt is driven.

3. Apparatus according to claim 1, said drive belt being made of elasticmaterial and having a profile corresponding to the profile of saidbeaded chain.

4. Apparatus according to claim 1, said beaded chain comprising a cord,sphere-like chain beads strung on said cord and having a diametercorresponding substantially to the inner diameter of said tubularhousing, tube-like beads strung on said cord in alternating relation tosaid sphere-like chain beads, said tube-like beads having a diameterless than said diameter of said sphere-like beads, and spring meanspositioned with respect to said beaded chain for holding said chaintaut.

5. Apparatus according to claim 4, said cord being made of elasticmaterial.

6. Apparatus according to claim 4, said cord being made of an inelasticmaterial, said spring means being a spring preloaded and disposedbetween the end of said cord and said beads.

7. Apparatus according to claim 6, said cord being made of steel.

1. Filling apparatus for inserting into long envelope tubes a material,such as nuclear fuel, in the form of pellets having a diameter thatensures a close fit with respect to the inner wall of the envelope tube,said apparatus comprising a magazine for holding a large number ofstacks of the pellets, a guide structure connectable to said magazinefor holding and guiding said stacks individually, and insertion means inoperative proximity to said guide structure for inserting the stackdiposed in said guide structure into an envelope tube to be filled, saidinsertion means including a tubular housing having a curved shape,flexible elongated insertion means slidably disposed in said housing,said insertion means comprising a beaded chain having a curved shape,and drive means engaging said insertion means for reciprocally movingsaid insertion means into the envelope tube to move said tablet stackfrom said guide structure into the envelope tube to a selected locationtherein, each successive stack being moved individually by saidinsertion means into the envelope tube, said drive means including adrive belt in lateral engagement with said chain.
 2. Apparatus accordingto claim 1, said drive means including a second drive belt, a slippingclutch, and a drive mechanism coupled with at least one of said drivebelts via said clutch, said drive mechanism including control means forcontrolling the speed at which said one drive belt is driven. 3.Apparatus according to claim 1, said drive belt being made of elasticmaterial and having a profile corresponding to the profile of saidbeaded chain.
 4. Apparatus according to claim 1, said beaded chaincomprising a cord, sphere-like chain beads strung on said cord andhaving a diameter corresponding substantially to the inner diameter ofsaid tubular housing, tube-like beads strung on said cord in alternatingrelation to said sphere-like chain beads, said tube-like beads having adiameter less than said diameter of said sphere-like beads, and springmeans positioned with respect to said beaded chain for holding saidchain taut.
 5. Apparatus according to claim 4, said cord being made ofelastic material.
 6. Apparatus according to claim 4, said cord beingmade of an inelastic material, said spring means being a springpreloaded and disposed between the end of said cord and said beads. 7.Apparatus according to claim 6, said cord being made of steel.